With  the  Compliments  of  the  Anther.  M 

'ihelvtMis 


CONTRIBUTIONS 


from  the 


CHEMICAL  LABORATORY  OF  HARVARD 

COLLEGE. 


By  HENRY  B.  HILL. 


[Reprinted  from  the  Proceedings  of  the  American  Academy' 
of  Arts  and  Sciences.] 


\ 


m 


OF  ARTS  AND  SCIENCES. 


125 


X. 

CONTRIBUTIONS  FROM  THE  CHEMICAL  LABORATORY 
OF  HARVARD  COLLEGE. 

By  Henry  B.  Hill. 


Presented  February  1,  1882. 


I.  On  Dibromacrylic  Acid. 

In  a communication  upon  furfurol  and  certain  of  its  derivatives 
which  I laid  before  the  Academy  a year  ago,  I described  a dibro- 
macrylic acid  * which  O.  R.  Jackson  and  I had  some  time  before  ob- 
tained from  mucobromic  acid  by  the  action  of  alkalies.  Although  we 
had  not  been  able  to  prepare  the  acid  in  a state  of  perfect  purity,  still 
our  results  seemed  to  us  sufficient  for  its  identification,  and  since  it 
then  appeared  that  a more  extended  study  of  it  would  interfere  with 
other  investigators  in  the  same  field,  further  work  upon  it  had  been 
for  the  time  given  up.  Not  long  afterward  it  became  evident  that 
our  hesitation  upon  this  account  had  been  quite  unnecessary ; but  it 
was  not  until  recently  that  I was  able  to  take  up  again  the  study  of 
this  acid.  I have  now  obtained  results  which  correct  our  previous 
observations  in  several  important  particulars. 

For  the  preparation  of  the  acid  O.  R.  Jackson  and  I used 
chiefly  the  barium  salt,  which  crystallized  well  from  water  or  dilute 
alcohol,  and  which  gave  us  constant  analytical  results.  The  air-dried 
salt  lost  nothing  in  vacuo  over  sulphuric  acid,  or  when  heated  to  80°, 
and  the  percentage  of  barium  which  it  contained  agreed  closely  with 
that  required  by  the  formula  Ba(C3HBr202)2.  We  therefore  with 
little  hesitation  considered  the  salt  anhydrous,  and  were  inclined  to 
ascribe  the  slight  loss  of  weight  which  we  noticed  at  100°  to  a slow 
decomposition.  The  acid  made  from  carefully-prepared  barium  salt 
crystallized  well,  melted  quite  sharply  at  83-84°,  but  on  analysis 


* These  Proceedings,  Vol.  XVI.  (n.  s.  viii.)  p.  192. 


126 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


proved  to  contain  too  high  a percentage  of  bromine.  Since  the  acid 
made  from  the  lead  salt  had  given  us  precisely  the  same  unsatisfactory 
results,  we  thought  it  probable  that  the  impurities  which  were  found 
in  the  acid  thus  made  were  introduced  by  a decomposition  of  the  acid, 
itself  in  its  liberation  from  its  salts.  A more  careful  study  of  this 
reaction  subsequently  convinced  me,  however,  that  such  was  not  the 
case.  Certainly  no  carbonic  dioxide,  bromacetylen,  or  hydrobromic 
acid  could  be  detected  as  resulting  from  such  decomposition  when 
dilute  sulphuric  acid  was  added  in  slight  excess  to  a boiling  aqueous 
solution  of  the  barium  salt.  I therefore  turned  my  attention  to  a 
further  purification  of  the  salts. 

Since  repeated  recrystallization  of  the  barium  salt  failed  to  give  me 
any  much  better  product,  I thought  it  worth  while  to  determine  the 
variation  of  composition  introduced  by  one  set  of  crystallizations  from 
water.  I therefore  dissolved  30  grammes  of  white  well-crystallized 
salt  (A)  in  380  cc.  of  hot  water.  On  cooling  6.5  grms.  of  the  salt 
(I.)  separated,  and  by  successive  filtration,  evaporation,  and  cooling 
I obtained  the  fractions  (II.)  8.9  grms.,  (III.)  6.9  grms.,  and  (IV.) 
4.8  grms.,  the  remaining  2.9  grms.  being  lost  in  the  filter-papers 
upon  which  the  successive  portions  were  dried.  An  analysis  of  these 
air-dried  salts  gave  the  following  results : — 

A.  0.5669  grm.  substance  gave  0.2239  grm.  BaS04. 

I.  0.5713  grm.  substance  gave  0.2276  grm.  BaS04. 

II.  0.5139  grm.  substance  gave  0.2036  grm.  BaS04. 

III.  0.5665  grm.  substance  gave  0.2231  grm.  BaS04 . 

IV.  0.5003  grm.  substance  gave  0.1941  grm.  BaS04 . 

Calculated  for  Calculated  for  Found. 

Ba(C3HBr202)2.  Ba(C3HBr202)2.H20.  A.  I.  H.  III.  IV. 

Ba  23.03  22.35  23.21  23  43  23.29  23.15  22.80 

From  these  results  it  was  evident  that  the  barium  salt  contained  a 
persistent  impurity  which  could  not  be  removed  by  fractional  crys- 
tallization, and  that  the  constancy  of  its  composition  was  accidental. 
I next  tried  the  beautifully  crystalline  acid  potash  salt  which  I have 
already  described,*  and  found  that  it  gave  results  which  were  all  that 
could  be  desired.  This  salt  can  easily  be  made  by  neutralizing  a 
weighed  amount  of  the  ordinary  acid  melting  at  82—84°  with  potassic 


* Loc.  cit.  p.  194. 


OF  ARTS  AND  SCIENCES. 


127 


carbonate,  and  adding  to  the  hot  solution  an  equal  amount  of  the  acid 
dissolved  in  a little  hot  water.  As  the  solution  cools  the  salt  separ- 
ates in  long  silky  needles,  which  after  a few  recrystallizations  from  hot 
water  yield  an  acid  whose  melting-point  is  constant.  The  loss  in 
recrystallization  is  comparatively  small,  since  the  salt  is  but  sparingly 
soluble  in  cold  water  and  dissolves  very  freely  in  hot.  The  analyses 
which  I have  made  of  the  acid  prepared  in  this  way  show  its  perfect 
purity. 

I.  0.2183  grm.  substance  gave  by  the  method  of  Carius  0.3573 

grm.  AgBr. 

II.  0.2127  grm.  substance  gave  0.3476  grm.  AgBr. 

III.  0.2530  grm.  substance  gave  0.4137  grm.  AgBr. 

Calculated  for  C3H2Br202.  Found. 

I.  II.  III. 

Br.  69.56  69.66  69.56  69.60 

The  pure  acid  melts  at  85.5-86°,  but  in  other  respects  does  not  differ 
essentially  in  its  physical  properties  from  the  product  which  I have 
already  described.  The  solubility  of  the  acid  was  determined  by 
neutralizing  with  baric  carbonate  an  aqueous  solution  of  the  acid 
prepared  according  to  the  method  of  V.  Meyer,  and  precipitating 
with  sulphuric  acid  the  barium  dissolved. 

I.  12.7854  grms.  of  a solution  saturated  at  17°. 5 gave  0.3107  grm. 

BaS04 . 

II.  13.5723  grms.  of  a solution  saturated  at  17°.5  gave  0.3303  grm. 

BaS04 . 

III.  10.8488  grms.  of  a solution  saturated  at  18°  gave  0.2695  grm. 

BaS04 . 

IV.  9.7341  grms.  of  a solution  saturated  at  18°  gave  0.2434  grm. 

BaS04 . 

According  to  these  determinations  the  aqueous  solution  saturated 
at  17°.5  and  18°  contains  the  following  percentages  : — 

17°.5.  18°. 

I.  II.  III.  IV. 

4.80  4.81  4.90  4.94 

Baric  Dibromacrylate , Ba(C3HBr202)2 . H20.  The  barium  salt 
prepared  by  neutralizing  a solution  of  the  pure  acid  with  baric  car- 


128 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


bonate  did  not  differ  in  outward  appearance  from  the  salt  made  directly 
from  mucobromic  acid  by  the  action  of  baric  hydrate,  but  proved  on 
analysis  to  contain  a percentage  of  barium  materially  lower  than  that 
which  O.  R.  Jackson  and  I had  previously  obtained,  and  closely  agree- 
ing with  that  required  by  one  molecule  of  water  of  crystallization. 
When  dried  by  exposure  to  the  air  the  salt  lost  nothing  over  sulphuric 
acid  or  when  heated  to  85°,  but  by  long-continued  heat  at  100°  (75  to 
100  hours)  or  more  rapidly  at  120°  it  gave  up  its  crystal  water  with- 
out showing  any  signs  of  decomposition. 

I.  0.6642  grm.  of  the  air-dried  salt  gave  by  precipitation  0.2540 
grm.  BaS04 . 

II.  0.6392  grm.  of  the  air-dried  salt  gave  on  ignition  with  H2S04 
0.2434  grm.  BaS04 . 

III.  0.5300  grm.  of  the  air-dried  salt  lost  at  120°  0.0161  grm.  H20. 

IV.  1.9253  grm.  of  the  air-dried  salt  lost  at  100°  0.0548  grm.  H20. 

V.  1.1582  grm.  of  the  air-dried  salt  lost  at  100°  0.0351  grm.  H20, 

and  gave  by  precipitation  with  II2S04  0.4408  grm.  BaS04 . 

Calculated  for  Ba(C3HBr202)o  • HzO.  Found. 

I.  II.  III.  IV. 

Ba  22.35  22.48  22.39 

II20  2.94  3 04  2.85 

The  solubility  of  the  salt  was  also  determined. 

I.  9.4276  grm.  of  an  aqueous  solution  saturated  at  18°  gave  by 
precipitation  0.2214  grm.  BaS04 . 

II.  8.4088  grm.  of  a solution  saturated  at  18°  gave  0.1917  grm. 
BaS04 . 

According  to  these  determinations  the  aqueous  solution  of  the  salt 
saturated  at  18°  contains  the  following  percentages  of  the  anhydrous 
salt : — 

I.  II. 

6.00  5.82 

Plumbic  Dibrom acrylate,  Pb(C3HBr202)2 . H20.  The  lead  salt 
which,  according  to  the  analyses  made  of  former  preparations,  was 
anhydrous  when  made  from  the  pure  acid  by  neutralization  with  plum- 
bic carbonate,  or  from  the  acid  potassium  salt  by  precipitation  with 
plumbic  acetate,  likewise  proved  to  contain  one  molecule  of  water  of 
crystallization. 


V. 

22.38 

3.03 


C 


OF  ARTS  AND  SCIENCES. 


129 


■ 


I.  0.5972  grm.  of  the  air-dried  salt  lost  at  100°  0.0161  grm.  H20, 

and  gave  by  ignition  with  H2S04  0.2655  grm.  PbS04. 

II.  1.0438  grm.  substance  dried  over  II2S04  lost  at  100°  0.0283  grm. 

H20,  and  gave  by  ignition  with  H2S04  0.4622  grm.  PbS04 . 

Calculated  for  Pb(C3HBr202).> . IPO.  . Found. 

I.  II. 

Pb  30.31  30.37  30.25 

H20  2.64  2.70  2.71 

Calcic  Dibromacrylate , Ca(C3HBr202)2 . 3H20.  The  calcium  salt 
made  from  the  pure  acid  crystallized  in  long  clustered  needles,  which 
gave  on  analysis  results  identical  with  those  which  O.  R.  Jackson  and 
I formerly  obtained. 

I.  2.1502  grm.  of  the  air-dried  salt  lost  at  80-85°  0.2034  grm. 
H20. 

II.  1.2264  grm.  of  the  air-dried  salt  lost  at  95-100°  0.1171  grm. 

H20. 

III.  1.8124  grm.  of  the  air-dried  salt  lost  at  100°  0.1755  grm.  H20. 

Calculated  for  Ca(C3HBr202)  . 3H20.  Found. 

I.  II.  III. 

I420  9.78  9.46  9.55  9.68 

I.  0.4393  grm.  of  the  salt  dried  at  100°  gave  on  ignition  with  H2S04 
0.1199  grm.  CaS04. 

II.  0.6161  grm.  of  the  salt  dried  at  100°  gave  on  ignition  with  H2S04 
0.1674  grm.  CaS04  . 

Calculated  for  Ca(C3HBr202)2 . Found. 

I.  II. 

Ca  8.03  8.03  7.99 

Fotassic  Dibromacrylate , KC3HBr202.  The  analysis  of  the  potas- 
sum  salt  made  by  neutralizing  the  pure  acid  with  potassic  carbonate 
showed  that  it  was  anhydrous,  as  it  had  previously  been  described. 

I.  0.7334  grm.  of  the  salt  dried  over  II2S04  gave  on  ignition  with 
Ii2S04  0.2373  grm.  K2S04. 

II.  0.7507  grm.  of  the  salt  dried  over  H2S04  gave  0.2427  grm. 

k2so4. 

VOL.  XVII.  (n.  S.  IX.) 


9 


130 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Calculated  for  KC3HBr202  Found. 

I.  II. 

K 14.58  14.53  14.51 

Although  many  unsuccessful  attempts  had  previously  been  made  to 
prepare  brompropiolic  acid  in  a pure  state,  it  seemed  to  me  not  im- 
possible that  the  prolonged  action  of  alkalies  in  the  cold  might  remove 
from  the  dibromacrylic  acid  a molecule  of  hydrobromic  acid,  and  that 
a purer  product  might  thus  be  obtained.  I found,  however,  that  the 
reaction  was  extremely  slow,  at  least  with  baric  hydrate.  An  aqueous 
solution  which  contained  one  molecule  of  baric  hydrate  to  each  mole- 
cule of  dibromacrylic  acid  was  strongly  alkaline  even  after  standing 
for  fifteen  days,  and  gave  on  acidification  and  extraction  with  ether 
the  compound  of  brompropiolic  and  dibromacrylic  acids  which  has 
already  been  described.  After  recrystallization  from  ligroin  the  sub- 
stance melted  at  103°,  and  gave  on  analysis  the  following  result : — 

0.2535  grm.  substance  gave  0.3766  grm.  AgBr. 

Calculated  for  C6H3Br304  . Found. 

Br.  63.33  63.22 

Since  I had  before  noticed  that  this  intermediate  product  could  be 
obtained  from  dibromacrylic  acid  by  the  action  of  baric  hydrate  in  the 
course  of  a few  hours,  and  that  malonic  acid  was  formed  even  in  the 
cold  after  the  lapse  of  several  months,  it  was  evident  that  further 
attempts  in  this  direction  were  useless. 


OP  ARTS  AND  SCIENCES, 


131 


II.  On  the  Crystalline  Form  op  a Dichloracrylic  Acid. 


By  W.  H.  Melville. 


(Communicated  by  H.  B.  Hill.) 


Although  the  physical  properties  of  the  dichloracrylic  acid  of 
Wallach  * are  decidedly  different  from  those  which  W.  Z.  Bennett 
and  I found  to  be  characteristic  of  the  dichloracrylic  acid  made  from 
mucochloric  acid,f  a difference  which  appeared  to  be  fully  confirmed 
by  a comparison  of  the  salts  of  the  two  acids,  still  it  seemed  to  me 
desirable  to  prove  with  a little  more  precision  the  difference  between 
the  two.  Since  Wallach  had  made  no  determinations  of  the  solubility 
of  his  acid  or  its  salts,  and  moreover  thought  $ that  little  weight 
should  be  attached  to  the  determinations  of  crystal-water  which  he 
had  as  yet  published,  there  remained  no  definite,  well-established 
points  of  difference  except  the  melting-points  (86°  and  77°)  and  a 
difference  in  the  crystalline  form  of  the  potassium  salt : one  crystal- 
lizing in  needles,  the  other  in  hexagonal  plates.  Since  the  |S  acid  had 
been  obtained  in  measurable  crystals  and  fully  described  in  Wallach’s 
first  paper,  although  we  had  previously  been  unable  to  get  measurable 
crystals  of  our  acid,  I made  fresh  attempts  with  larger  quantities  of 
material  than  had  then  been  at  our  disposal.  I found  that  by  the 
slow  cooling  of  a warm,  moderately  dilute  solution  in  chloroform  well- 
developed  crystals  could  be  obtained,  although  the  determination  of 
the  crystals  was  rendered  difficult  on  account  of  the  rapid  roughening 
of  their  faces  when  exposed  to  the  air.  Dr.  W.  H.  Melville  succeeded, 
however,  in  making  the  necessary  measurements,  and  to  his  kindness 
I am  indebted  for  the  following  description.  The  purity  of  the 
material  used  was  determined  by  analysis. 

0.2061  grm.  of  the  substance  gave  0.4198  grm.  AgCl. 


Calculated  for  C3H2CI2O2 . 

Cl.  50.36 


Found. 

50.35 


* Ann.  Chem.  u.  Pharm.  vol.  cxciii.  19. 
t These  Proceedings,  Vol.  XVI.  (n.  s.  viii.)  p.  206. 
J Ann.  Chem.  u.  Pharm.  cciii.  83. 


132 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Crystalline  form  of  Dichloracrylic  Acid.  * 


Orthodiagonal  b = 1 

Vertical  Axis  c = 0.3637 

Angle  of  Axes  XZ  = 87°  32' 


Angles  between  Normals. 


Observed. 

Ill  and  III  = 37°  54') 
Til  “ 001  = 25°  8'  l 
Til  “ TOO  = 71°  49' ) 
001  “ TOO  = 87°  32' 
TOO  “ 110  = 49°  56' 
T10  “ 110  = 80°  6' 


Calculated. 

Fundamental  angles. 

87°  33' 

49°  51' 

80°  18' 


Although  Wallach’s  dichloracrylic  acid  also  crystallizes  in  the  mono- 
clinic system,  the  forms  are  totally  unlike,  and  the  difference  between 
the  two  acids  is  therefore  established. 


OF  ARTS  AND  SCIENCES. 


133 


III.  On  the  Relation  between  Dibromacrylic  Acid  and 
Tribrompropionic  Acids. 

By  Henry  B.  Hill  and  Clement  W.  Andrews. 

Nearly  two  years  ago  Michael  and  Norton  * * * § published  a description 
of  the  tribrompropionic  acid  melting  at  92°  which  was  first  mentioned 
by  Linnemann  and  Penl,t  and  which  they  obtained  by  the  addition 
of  bromine  to  the  so-called  ft  monobromacrylic  acid  of  Tollens  and 
Wagner.  In  this  paper  they  remarked  that  potassic  hydrate  attacked 
the  acid  readily  in  alcoholic  solution,  but  they  attempted  no  isolation 
of  the  dibromacrylic  acid  which  was  thus  formed.  They  soon  after- 
wards offered  to  relinquish  the  farther  study  of  this,  acid,  in  case  we 
felt  interested  to  undertake  its  preparation  and  comparison  with  the 
dibromacrylic  acid  which  one  of  us  had  already  described.  This  kind 
offer  was  accepted,  and  we  began  the  investigation  at  once.  Although 
we  had  no  difficulty  in  the  isolation  of  a dibromacrylic  acid  which 
closely  resembled  that  which  had  been  made  from  mucobromic  acid, 
still  it  was  impossible  to  establish  the  identity  of  the  two  until  the 
latter  had  been  somewhat  more  carefully  studied.  In  the  mean  time 
Mauthner  and  Suida,  $ in  an  article  upon  substituted  acrylic  and  pro- 
pionic acids,  described  again  the  preparation  of  the  tribrompropionic 
acid  melting  at  92°,  without  having  seen  more  than  a brief  notice  of 
Michael  and  Norton’s  work.  In  this  article  they  further  showed  that 
it  might  be  converted  by  the  action  of  potassic  hydrate  into  a dibrom- 
acrylic acid,  which,  as  they  asserted,  was  identical  with  that  which 
O.  R.  Jackson  and  one  of  us  had  obtained  from  mucobromic  acid.§ 
The  only  facts  which  they  brought  forward  in  support  of  this  assertion 
were,  the  melting-point,  85°,  the  ready  formation  of  malonic  acid  by 
the  action  of  baric  hydrate,  and  the  anhydrous  form  of  the  lead  salt. 
Since  neither  the  melting-point  nor  the  action  of  baric  hydrate  will 
discriminate  between  the  two  isomeric  forms  of  dibromacrylic  acid 
already  known,  and  moreover  since  the  lead  salt  of  one  of  these  two 
acids  has  never  been  described  and  of  the  other  is  not  anhydrous,  as 
one  of  us  has  recently  shown,  it  is  evident  that  these  facts  were  wholly 
insufficient  to  characterize  the  acid  in  question.  Our  investigation  of 


* Amer.  Chem.  Journ.  ii.  18. 

t Berichte  der  deutsch.  chem.  Gesellseh.,  viii.  1098. 

f Sitzungsberichte  der  kk.  Akademie,  Wien,  lxxxiii.  273. 

§ These  Proceedings,  Vol.  XVI.  (n.  s.  viii.)  p.  192. 


134 


PROCEEDINGS  OF  THE  AMERICAN'*  ACADEMY 


the  same  acid  has  shown  us  that  their  assertion,  though  unsupported 
by  evidence,  was  accidentally  correct. 

Dibromacrylic  Acid , C3H2Br202 . In  the  preparation  of  the  tri- 
brompropionic  acid  necessary  for  this  research  we  followed  quite 
closely  the  method  of  Michael  and  Norton,  although  we  did  not  con- 
sider it  necessary  to  purify  the  dibrompropyl  alcohol  by  distillation 
under  diminished  pressure  before  oxidation.  For  the  conversion  of 
the  tribrompropionic  acid  into  the  corresponding  dibromacrylic  acid 
we  have  found  it  most  advantageous  to  dissolve  it  in  the  calculated 
amount  of  a titrated  solution  of  baric  hydrate,  and  to  allow  the 
reaction  to  proceed  at  ordinary  temperatures.  After  standing  for 
several  days  the  neutral  or  at  most  feebly  alkaline  solution  was  evap- 
orated, and  the  acid  extracted  from  the  recrystallized  barium  salt  thus 
obtained.  Since  this  acid  was  found  by  preliminary  trial  to  give  a 
sparingly  soluble  acid  potassium  salt  which  crystallized  in  long  silky 
needles,  for  further  purification  it  was  converted  into  this  salt.  After 
several  recrystallizations  from  hot  water,  the  acid  was  set  free  by  the 
addition  of  hydrochloric  acid  and  extracted  with  ether.  The  acid  thus 
obtained  crystallized  in  small  oblique  prisms  readily  soluble  in  alcohol, 
ether,  and  chloroform,  more  sparingly  in  benzol  or  carbonic  disulphide. 
Under  water  the  crystals  melted  at  about  20°  to  a colorless  oil  which 
dissolved  readily  on  heating.  The  acid  dried  over  sulphuric  acid 
melted  at  85-86°,  and  gave  on  analysis  percentages  corresponding  to 
the  formula  C3H2Br202 . 

I.  0.7497  grm.  substance  gave  on  combustion  0.4341  grm.  C02  and 
0.0673  grm.  H20 . 

II.  0.2863  grm.  substance  gave  0.4691  grm.  AgBr. 

III.  0.2093  grm.  substance  gave  0.3432  grm.  AgBr. 


Calculated  for  C3EL>Br202 . 

Found. 

I. 

II. 

III. 

c 

15.65 

15.79 

H 

0.87 

1.00 

Br 

69.56 

69.72 

69.84 

The  solubility  of  the  acid  we  determined  by  neutralizing  with  baric 
carbonate  an  aqueous  solution  prepared  according  to  the  method  of 
V.  Meyer  and  determining  by  precipitation  the  barium  dissolved. 

I.  12.4640  grms.  of  a solution  saturated  at  18°  gave  0.3124  grm. 
BaS04 . 

II.  12.2745  grms.  of  a solution  saturated  at  18°  gave  0.3091  grm. 
BaS04. 


OF  ARTS  AND  SCIENCES. 


135 


According  to  these  determinations  the  aqueous  solution  saturated  at 
18°  contained  the  following  percentages:  — 

I.  II. 

4.95  4.97 

Baric  Dibromacrylate , Ba(C3HBr202)2 . H20.  The  barium  salt  made 
by  neutralizing  a solution  of  the  acid  with  baric  carbonate  crystallized 
in  rhombic  plates  more  or  less  irregular  in  form,  which  when  dried  by 
exposure  to  the  air  contained  one  molecule  of  water. 

I.  1.3641  grm.  of  salt  dried  over  H2S04  gave  by  precipitation 
0.5195  grm.  BaS04 . 

II.  3.1482  grms.  of  the  air-dried  salt  lost  at  110°  0.0933  grm.  H20; 
0.8202  grm.  of  the  same  air-dried  salt  gave  by  precipitation 
0.3147  grm.  BaS04 . 

III.  1.7219  grm.  of  salt  dried  over  H2S04  lost  at  120°  0.0520  grm. 
H20 ; 0.6769  of  the  same  salt  gave  by  precipitation  0.2555 
grm.  BaSO. . 


Calculated  for  Ba(  C3HBr202)2  . II20  . 

I. 

Ba  22.35  22.40 

H20  2.94 


Found. 

II. 

22.56 

2.96 


III. 

22.19 

3.02 


For  its  further  identification  we  determined  its  solubility  in  water 
at  18°. 

9.2373  grm.  of  a solution  saturated  at  18°  gave  by  precipitation 
0.2131  grm.  BaS04. 

From  this  determination  it  follows  that  the  aqueous  solution  satu- 
rated at  18°  contained  5.89%  of  the  anhydrous  salt. 

Calcic  Dibromacrylate,  Ca(C3HBr202)2 . 3H20.  The  calcium  salt 
crystallized  in  clustered  needles  which  contained  three  molecules  of 
water  of  crystallization  when  dried  by  exposure  to  the  air. 

I.  0.5761  grm.  of  the  air-dried  salt  lost  at  80°  0.0535  grm.  II20. 

II.  0.5101  grm.  of  the  air-dried  salt  lost  at  80°  0.0491  grm.  H20. 

Calculated  for  Ca(C3HBr202)2 . 3H20.  Found. 

9.78 


H20 


I. 

9.29 


II. 

9.63 


0.4608  grm.  of  the  salt  dried  at  80°  gave  on  ignition  with  H2S04 
0.1262  grm.  CaS04. 


136  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

Calculated  for  Ca(C3HBr202)2.  Found. 

Ca  8.03  8.06 

Potassic  Dibromacrylate , KC3HBr202.  The  potassium  salt  was 
made  from  the  acid  by  neutralization  with  potassic  carbonate.  It 
crystallized  in  leafy  plates  which  were  anhydrous. 

0.6842  grm.  of  the  air-dried  salt  gave  on  evaporation  with  H2S04 
and  ignition  0.2229  grm.  K2S04 . 

Calculated  for  KC3HBr202  Found. 

K 14.58  14.62. 

A comparison  of  these  results  with  those  which  one  of  us  has  pre- 
sented in  the  preceding  paper  will  be  facilitated  by  the  following 
table,  which  gives  the  mean  of  each  series  of  results : — 


Dibromacrylic  Acid  from 

Mucobromic 

Tribrompropionic 

Melting-point 

Aqueous  solution  18°,  % acid 

Barium  salt,  % water 

Barium  salt  solubility  18°  

Calcium  salt,  % water 

85.5-86° 

4.92 

2.97 

5.91 

9.56 

85-86° 

4.96 

2.99 

5.89 

9.46 

Since  the  identity  of  the  dibromacrylic  acid  formed  by  the  sub- 
traction of  hydrobromic  acid  from  the  tribrompropionic  acid  melting 
at  92°  with  that  derived  from  mucobromic  acid  was  thus  established 
with  precision,  it  seemed  to  us  of  interest  to  study  a little  more  closely 
the  tribrompropionic  acid  which  this  same  dibromacrylic  acid  forms 
by  the  addition  of  hydrobromic  acid.  Mr.  C F.  Mabery  * had  with 
one  of  us  already  proved  that  such  an  addition  product  could  be  formed, 
but  it  had  been  prepared  solely  from  the  impure  acid  melting  at  83- 
84°  and  very  little  studied.  We  therefore  at  first  undertook  its  prep- 
aration in  larger  quantity  from  pure  acid  melting  at  85-86°. 

Tribrompropionic  Acid , C3H3Br302 . When  dibromacrylic  acid 
made  by  the  action  of  baric  hydrate  upon  mucobromic  acid  is  heated 
with  three  or  four  times  its  weight  of  hydrobromic  acid  saturated  at 
0°  for  eight  or  ten  hours,  at  100°  the  needle-like  prisms  disappear  and 
are  replaced  by  rectangular  plates  of  the  new  tribrompropionic  acid. 
With  the  pure  acid  no  carbonization  such  as  had  been  noticed  in  work- 
ing with  the  impure  acid  was  observed  even  at  120°,  and  we  therefore 


* These  Proceedings,  Vol.  XVI.  (n.  s.  vru.)  p.  197. 


OF  ARTS  AND  SCIENCES. 


137 


usually  allowed  the  addition  to  proceed  at  this  higher  temperature, 
since  the  reaction  was  then  completed  in  a shorter  time.  The  tubes 
opened  without  marked  pressure,  and  the  crystalline  product  separated 
from  the  acid  mother-liquors  by  filtration  upon  a perforated  platinum 
cone  was  dried  upon  porous  tiles.  When  treated  in  this  way  the 
dibromacrylic  acid  gave  about  its  own  weight  of  crude  tribrompro- 
pionic  acid.  The  acid  can  readily  be  purified  by  recrystallizing  it 
successively  from  ligroin  and  carbonic  disulphide.  The  use  of  car- 
bonic disulphide  causes  considerable  loss,  but  with  ligroin  alone  we 
failed  to  obtain  as  high  a melting-point.  After  several  recrystalliza- 
tions the  acid  showed  a constant  melting-point,  and  gave  on  analysis 
the  required  percentages. 

I.  1.0329  grm.  substance  dried  over  H2S04  gave  on  combustion 
0.4446  grm.  C02  and  0.0994  grm.  H20. 

II.  0.2184  grm.  substance  gave  0.3963  grm.  AgBr. 

III.  0.1938  grm.  substance  gave  0.3525  grm.  AgBr. 


c 

Calculated  for  C3H3Br302 . 

11.57 

I. 

11.74 

Found. 

II. 

H 

0.96 

1.07 

Br 

77.17 

77.29 

This  tribrompropionic  acid  is  very  soluble  in  alcohol  or  ether,  some- 
what less  soluble  in  chloroform,  carbonic  disulphide,  benzol  or  ligroin. 
It  dissolves  freely  in  hot  water,  but  is  quite  rapidly  decomposed  on 
boiling  with  the  formation  of  hydrobromic  acid.  From  the  hot  aque- 
ous solution  the  acid  crystallizes  on  cooling  in  pearly  scales.  Repeat- 
edly recrystallized  from  carbonic  disulphide,  the  acid  melts  at  118°. 

Argentic  Tribrompropioncite,  AgC3H2Br302.  Argentic  nitrate  added 
to  a cold  aqueous  solution  of  the  acid  precipitates  the  silver  salt  in 
small  clustered  rhombic  plates.  On  warming  it  with  water  argentic 
bromide  is  rapidly  formed,  but  it  may  be  dried  over  sulphuric  acid 
without  essential  decomposition. 

0.2901  grm.  of  the  salt  dried  over  H2S04  gave  by  precipitation  with 
HBr  0.1316  grm.  AgBr. 

Calculated  for  AgC3H2Br302 . Found. 

Ag  25.83  26.05 

The  barium  and  calcium  salts  were  readily  soluble  in  water,  and 
their  solutions  could  not  be  warmed  without  the  instantaneous  forma- 


138 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


tion  of  bromide.  Even  on  evaporating  their  solutions  at  ordinary 
temperatures  over  sulphuric  acid  in  vacuo  the  barium  salt  was  almost 
wholly  decomposed ; the  calcium  salt  was  apparently  somewhat  more 
stable,  for  it  was  thus  obtained  in  dendritic  needles,  although  the  mother- 
liquor  contained  calcic  bromide.  Since  the  air-dried  salt  lost  nothing 
over  sulphuric  acid  and  was  decomposed  by  heat,  the  water  of  crys- 
tallization could  not  be  directly  determined.  It  gave,  however,  a per- 
centage of  calcium  agreeing  closely  with  that  required  by  two 
molecules  of  water. 

I.  1.1087  grm.  of  the  air-dried  salt  gave  on  ignition  with  H2S04 
0.2179  grm.  CaS04. 

II.  0.7279  grm.  of  the  air-dried  salt  gave  on  ignition  with  H2S04 
0.1425  grm.  CaS04 . 

Calculated  for  Ca(C3H2Br302).2.  2H20. 

Ca  5.75 

We  were  unable  to  prepare  other  salts. 

Dibromacrylic  Acid.  The  ready  decomposition  of  the  tribrompro- 
pionic  acid  made  it  seem  desirable  to  isolate  and  identify  the  dibrom- 
acrylic acid  which  was  thus  formed.  For  this  purpose  we  dissolved 
pure  tribrompropionic  acid,  melting  at  118°,  in  water  and  added  from 
a burette  a titrated  solution  of  baric  hydrate.  So  rapid  was  the 
action  that  an  alkaline  reaction  could  not  be  maintained  until  nearly 
one  molecule  of  baric  l^drate  had  been  added  for  each  molecule  of 
the  acid.  When  the  calculated  amount  of  baric  hydrate  had  been 
added  the  solution  was  allowed  to  stand  for  half  an  hour,  and  then 
but  a trace  of  baric  carbonate  could  be  precipitated  with  carbonic 
dioxide.  Ether  extracted  from  the  acidified  solution  a crystalline 
acid  melting  at  85-86°,  which  gave  on  analysis  the  percentage  of 
bromine  required  by  the  formula  C3II2Br202 . 

0.1979  grm.  substance  gave  0.3240  grm.  AgBr. 

Calculated  for  C3H2Br202 . Found. 

Br.  69.57  ~ **  69.66. 

The  solubility  of  the  acid  in  cold  water  was  determined  by  the 
method  of  V.  Meyer. 

I.  10.7793  grms.  of  a solution  saturated  at  18°  gave  on  neutralization 
with  baric  carbonate  and  precipitation  0.2908  grm.  BaS04 . 
II.  7.7354  grms.  of  a solution  saturated  at  18°  gave  0.1940  grm. 
BaS04 . 


Found. 

I.  II. 

5.78  5.76 


OF  ARTS  AND  SCIENCES. 


139 


> 


According  to  these  determinations  the  aqueous  solution  of  the  acid 
saturated  at  18°  contained  the  percentages  : — 

I.  II. 

5.32  4.95 

Baric  Dibromacrylate,  Ba(C3HBr202)2 . H20.  By  neutralizing  the 
acid  with  baric  carbonate,  or  more  conveniently  by  the  direct  evapo- 
ration of  the  solution  obtained  by  the  action  of  baric  hydrate  upon 
tribrompropionic  acid,  we  obtained  the  barium  salt  in  leafy  rhombic 
plates  which,  when  dried  over  sulphuric  acid,  contained  one  molecule 
of  water. 

I.  1.1489  grm.  of  the  salt  dried  over  II2S04  lost  at  100-105°  0.0335 
grm.  H20. 

II.  1.5158  grm.  of  the  salt  dried  over  H2S04  lost  at  105-110°  0.0457 
grm.  !I20,  and  gave  on  precipitation  0.5790  grm.  BaS04. 


Calculated  for  Ba(C3IIBr202)2 . H20  . 

Found. 

I.  II. 

Ba  22.35 

22.46 

H20  2.94 

2.92  3.02 

Calcic  Dibromacrylate,  Ca(C3HBr202)2 . 3 H20.  The  calcium  salt 
crystallized  in  radiating  needles  which  contained  when  air-dried  three 
molecules  of  water. 

0.9444  grm.  of  the  air-dried  salt  lost  at  100-105°  0.0906  grm.  H20, 
and  gave  on  ignition  with  H2S04  0.2332  grm.  CaS04 . 

Calculated  for  Ca(C3HBr202)  2-  3 H20 . Found. 

Ca  7.25  ~ 7.26 

H20  9.78  9.59 


These  results  are  sufficient  to  prove  that  this  dibromacrylic  acid  is 
identical  with  the  one  already  studied,  as  a comparison  of  the  mean 
results  given  in  the  following  table  will  show. 


Dibromacrylic  Acid  from 

Mucobromic  Acid. 

Tribrompropionic. 

Melting-point 

85.5-86° 

4.92 

2.97 

9.56 

85-86° 

5.12 

2.97 

9.59 

Aqueous  solution  saturated  at  18°,  acid 

Barium  salt,  % water 

Calcium  salt,  % water  

140 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


IV.  On  Certain  Tetrasubstituted  Propionic  Acids. 

By  Henry  B.  Hill  and  Charles  E.  Mabery. 

In  a previous  communication  * one  of  us  has  already  mentioned  the 
fact  that  the  dibromacrylic  from  mucobromic  acid,  unlike  the  dichlor- 
acrylic  acid  of  Wallach,  takes  up  a molecule  of  bromine  with  readiness 
and  forms  a tetrabrompropionic  acid.  We  were  led  to  undertake  a 
more  complete  study  of  the  tetrasubstituted  propionic  acids,  especially 
with  the  hope  that  the  study  of  those  containing  two  different  halo- 
gens might  throw  some  light  upon  the  position  of  the  halogen  atoms 
in  the  disubstituted  acrylic  acids  formed  from  mucobromic  and  muco- 
chloric  acids.  After  our  investigations  were  concluded  Mauthner  and 
Suida  t published  in  the  Proceedings  of  the  Vienna  Academy  a paper 
entitled  “ Ueber  gebromte  Propionsauren  und  Acrylsauren,”  in  which 
they  anticipate  us  in  the  publication  of  a portion  of  our  work.  Since 
they  were  perfectly  well  aware  that,  in  studying  derivatives  of  a sub- 
stituted acrylic  acid  which  they  asserted,  although  without  adequate 
proof,  was  identical  with  that  obtained  from  mucobromic  acid,  they 
were  trespassing  upon  ground  which  one  of  us  had  already  fully  re- 
served, we  think  it  advisable,  although  it  involves  a certain  amount  of 
repetition,  to  give  our  results  in  full,  more  especially  since  we  are  able 
to  correct  their  work  in  several  important  particulars. 

Tetrabrompropionic  Acid . 

Tetrabrompropionic  acid  can  readily  be  made  by  the  addition  of 
bromine  to  dibromacrylic  acid  at  ordinary  temperatures. $ We  have 
prepared  it  by  adding  to  a solution  in  chloroform  the  calculated  amount 
of  bromine.  On  standing,  the  addition  product  gradually  separates, 
often  in  large,  well -formed  prisms.  The  amount  of  the  product  thus 
obtained  was  about  90%  of  the  theoretical  yield.  After  recrystalliza- 
tion from  chloroform  the  substance  was  dried  over  sulphuric  acid. 


* These  Proceedings,  Vol.  XVI.  (n.  s.  viii.)  p.  197. 
t Sitzungsberichte  der  kk.  Akademie,  Wien,  lxxxiii.  273. 

X Mauthner  and  Suida  assert  that  the  dibromacrylic  acid  will  take  up  no 
bromine  in  the  cold.  They  prepared  tetrabrompropionic  acid  by  heating  to 
100°  with  undiluted  bromine.  That  the  bromine  is  very  readily  taken  up  one 
of  us  first  mentioned  several  years  ago  (Berichte  der  deutsch.  chem.  Gesellsch., 
1.  xii.  657). 


OF  ARTS  AND  SCIENCES. 


141 


I.  0.5480  grra.  substance  gave  0.1837  grm.  C02  and  0.0286  grm. 
H20. 

II.  0.1775  grm.  substance  gave  0.3432  grm.  AgBr. 


Calculated  for  C3H2Br402  . Found. 


I. 

II. 

' 

c 

9.23 

9.14 

4 

H 

0.51 

0.58 

Br 

82.04 

82.28 

Tetrabrompropionic  acid  crystallizes  in  prisms  of  the  triclinic  sys- 
tem which  melt  at  125-126°.  It  is  very  soluble  in  alcohol  or  ether, 
readily  soluble  in  hot  chloroform,  carbonic  disulphide  or  benzol,  and 
separates  in  crystals  as  these  solutions  cool.  In  ligroin  it  is  sparingly 
soluble.  Under  water  it  melts  at  a very  low  temperature  to  a color- 
less oil  which  dissolves  freely  on  heating. 

For  a crystallographic  study  of  the  substance  we  are  indebted  to 
Dr.  W.  H.  Melville. 

Crystalline  Form  of  Tetrabrompropionic  Acid. 


Triclinic  System. 

Forms,  $100}  $010}  {001}  {011}  $1T0}. 


Elements  : Macrodiagonal  a = 1.507 

Brachydiagonal  b = 1 

Vertical  Axis  c = 0.934 

Angles  of  Axes  XY  ==  94°  59' 

XZ  = 104°  28' 
YZ  = 74°20/ 


142 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Angles  between  Normals. 


Observed. 

100  and  010  = 88°  48' 

010  “ Oil  = 56°  3' 

011  “ 001  = 48°  51^  ► 
100  “ Oil  = 77°  21Jr 
100  “ 1T0  = 57°  25 ' 
100  “ 001  = 77°  1' 


Calculated. 


Fundamental  angles. 


76°  21' 


Argentic  Tetrabrompropionate , AgC3HBr402 . Argentic  nitrate 
added  to  a solution  of  the  acid  in  dilute  alcohol  precipitates  the  silver 
salt  in  clustered  needles,  which  may  further  be  increased  in  quantity 
by  the  cautious  addition  of  ammonic  hydrate.  The  salt  is  extremely 
unstable,  forms  argentic  bromide  on  warming,  and  blackens  rapidly 
in  diffused  light. 

1.2182  grm.  of  the  salt  dried  over  H2S04  gave  0.4744  grm.  AgBr. 

Calculated  for  AgC3HBr402 . Found. 

Ag  21.78  22.38 

Baric  Tetrabrompropionate , Ba(C3HBr402)2 . 2HaO.  An  aqueous 
solution  of  the  acid  dissolved  baric  carbonate  readily  in  the  cold,  and 
if  the  solution  was  not  warmed  there  was  no  noticeable  decomposition. 
On  spontaneous  evaporation  at  ordinary  temperatures  the  barium  salt 
was  left  in  clusters  of  flattened  needles.  When  dried  by  exposure  to 
the  air  they  contained  two  molecules  of  water  which  they  lost  over 
sulphuric  acid. 

I.  0.7239  grm.  of  the  air-dried  salt  lost  over  H2S04  0.0272  grm. 
H20. 

II.  0.7087  grm.  of  the  air-dried  salt  lost  over  H2S04  0.0259  grm. 
H20. 

Calculated  for  Ba(  C3HBr402)2 . 2H20.  Found. 

I.  II. 

H20  3.79  3.76  3.66 

0.6756  grm.  of  the  salt  dried  over  H2S04  gave  on  ignition  with 
H2S04  0.1742  grm.  BaS04 . 

Calculated  for  Ba(C3HBr402)2 . 

14.97 


Ba 


Found. 

15.16 


OF  ARTS  AND  SCIENCES. 


143 


Calcic  Tetrabrompropionate , Ca(C3HBr402)2 . The  calcium  salt, 
made  by  neutralizing  an  aqueous  solution  of  the  acid  with  calcic  car- 
bonate and  allowing  the  solution  to  evaporate  spontaneously,  crys- 
tallized in  needles  which  proved  to  be  anhydrous.  The  salt  freed 
from  moisture  by  pressure  did  not  materially  lose  in  weight  when 
exposed  to  the  air,  and  when  air-dried  lost  nothing  over  sulphuric 
acid. 


I.  0.5065  grm.  of  the  salt  dried  over  H2S04  gave  on  ignition  with 
H2S04  0.0888  grm.  CaS04. 

II.  1.0886  grm.  of  the  salt  dried  over  H2S04  gave  0.1850  grm. 
CaS04 . 


Calculated  for  Ca(C3H2Br402)2. 
Ca  4.89 


Found. 

I.  II. 

5.16  5.00 


When  a solution  of  baric  tetrabrompropionate  was  heated  baric 
bromide  was  formed,  carbonate  dioxide  escaped,  and  at  the  same  time 
the  liquid  became  turbid  through  the  separation  of  a colorless  oil.* 
On  distilling  the  liquid  the  oil  passed  readily  over  with  steam,  and 
since  from  the  method  of  its  formation  there  could  be  little  doubt  that 
it  was  tribromethylen,  for  identification  it  was  immediately  converted 
into  its  dibromide  by  the  addition  of  bromine.  The  crystalline  addi- 
tion product  which  was  thus  obtained  when  purified  by  recrystallization 
melted  at  53°  and  gave  on  analysis  a percentage  of  bromine  which 
showed  it  to  be  pentabromethan. 

0.1696  grm.  substance  gave  0.3766  grm.  AgBr. 

Calculated  for  C2HBr5  . Found. 

94.12  94.48 


This  decomposition  may  therefore  be  expressed  by  the  equation : 

Ba(C3HBr402)2  = BaBr2  + 2 C02  + 2 C2HBr3. 

By  the  action  of  an  alcoholic  solution  of  potassic  hydrate  upon  tetra- 
brompropionic  acid  a molecule  of  hydrobromic  acid  is  removed,  and 
there  results  the  tribromacrylic  acid  melting  at  118°  which  we  have 


* Mauthner  and  Suida  assert  that  this  decomposition  also  takes  place  on  long 
standing  at  ordinary  temperatures.  They  were  therefore  able  to  isolate  no 
salts.  We  have  never  observed  any  decomposition  in  the  cold.  Loc.  cit. 
p.  284. 


144 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


already  described.* * * §  Dr.  W.  H.  Melville  kindly  made  a crystallo- 
graphic study  of  the  crystals  which  we  obtained,  and  established  their 
identity  with  those  he  had  previously  examined,  which  were  prepared 
by  the  addition  of  bromine  to  brompropiolic  acid.  A description  of 
the  crystalline  form  of  tribromacrylic  acid  Dr.  Melville  presents  in 
a separate  communication. 

a Dichlorbrompropionic  Acid. 

In  studying  the  dichloracrylic  acid  made  from  mucochloric  acid 
W.  Z.  Bennett  and  one  of  us  found  that  even  at  100°  it  would  not 
take  up  bromine  when  dissolved  in  chloroform.f  Subsequently  it 
appeared  from  the  experiments  of  C.  W.  Andrews  that  the  substituted 
propionic  acid  could  readily  be  made  by  the  action  of  undiluted  bro- 
mine, although  circumstances  at  the  time  prevented  a detailed  study 
on  his  part.  As  a precise  characterization  of  this  addition  product 
seemed  of  interest  we  undertook  its  preparation  and  investigation. 

Pure  dichloracrylic  acid  melting  at  85-86°  was  heated  with  a mol- 
ecule of  bromine  for  several  hours  at  100°.  The  almost  colorless 
product  of  the  reaction  was  pressed  thoroughly  with  paper  and  purified 
by  crystallization,  at  first  from  carbonic  disulphide,  and  finally  from 
chloroform.  When  dried  over  sulphuric  acid  this  substance  gave  on 
analysis  percentages  agreeing  closely  with  those  required  by  the  for- 
mula CH2Cl2Br202.  In  the  indirect  determination  of  the  halo- 
gens we  used  the  extremely  convenient  and  accurate  method  recently 
described  by  Mr.  L.  P.  Kinnicutt.l 

I.§  0.8124  grm.  substance  gave  0.3550  grm.  C02  and  0.0665  grm. 

h2o. 

II.  0.1715  grm.  substance  gave  0.3775  grm.  AgCl  -f-  AgBr. 

III.  0.4790  grm.  substance  gave  1.0559  grm.  AgCl  -j-  AgBr.  From 
this  by  reduction  was  obtained  0.6887  grm.  Ag. 


* These  Proceedings,  Yol.  XVI.  (n.  s.  viii.)  p.  216.  Mauthner  and  Suida 
assign  to  the  barium  and  calcium  salts  of  this  acid,  prepared  by  them  from  tetra- 
brompropionic  acid,  formulae  differing  greatly  from  those  which  we  formerly 
established  by  our  analyses.  Since  their  determinations  were  made  with 
small  quantities  of  material,  we  have  not  thought  it  necessary  to  make  further 
analyses  in  support  of  our  formulae. 

t These  Proceedings,  Vol.  XVI.  (n.  s.  viii.)  p.  211. 

J These  Proceedings,  Vol.  XVII. (n.  s.  xi.)  p.  91. 

§ These  analyses  were  made  by  Mr.  Andrews. 


OP  ARTS  AND  SCIENCES. 


145 


Calculated  for  C3H2Cl2Br202 . 

Found. 

I. 

II. 

c 

11.96 

11.91 

H 

0.67 

0.90 

Cl 

23.59 

Br 

53.15  76-74 

76.93 

This  a dichlordibrompropionic  acid  crystallizes  in  well-formed  tri- 
clinic  prisms,  which  melt  at  94-95°.  It  is  readily  soluble  in  water, 
alcohol,  or  ether ; in  carbonic  disulphide,  chloroform,  or  benzol  it  dis- 
solves less  freely.  From  a solution  in  carbonic  disulphide  it  could  be 
obtained  by  slow  evaporation  in  well-formed  crystals,  whose  study  was 
kindly  undertaken  by  Dr.  W.  H.  Melville. 


Crystalline  Form  of  a Dichlordibrompropionic  Acid. 


Triclinic  System. 

Forms,  {100}  {010}  {001}  {101}  {011}  {10T}  {0TT}  ; {110} 
and  ^110}  often  present. 


* Elements  : Macrodiagonal  a = 1.023 
Brachydiagonal  b = 1 
Vertical  axis  c = 1.052 
Angles  of  axes  XY  = 91° 

XZ  = 76°  31J' 
YZ  = 108°  52' 


* Through  an  error  the  ratios  of  the  fundamental  parameters  were  originally 
given  in  the  Berichte  der  deutsch.  chem.  Gesellsch.  xiv.  1680.  a : b : c = 
1.084  : 1 : 1.062. 

VOL.  XVII.  (N.  8.  IX.) 


10 


146 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Angles  between  Normals. 


Observed. 


Calculated. 


100  and  010  = 93°  37' 

100  “ 101  = 52°  58' 
010  “ Oil  = 34°  57' 

010  “ 101  = 77°  19' 

101  “ Oil  = 58°  46' 
100  “ 10T=  38°  32' 

011  “ 001  = 35°  21' 
001  “ Oil  = 55°  45' 
100  “ Oil  = 101°  3' 

100  “ Oil  = 98°  49' 

101  “ 101  = 87°  34' 
101  “ Oil  = 50°  32' 


y Fundamental  angles. 


38°  41' 
35°  52' 
55°  30' 
100°  39' 
98°  38' 
88°  20' 
50°  30' 


Argentic  a Dichlordibrompropionate , AgC3HCl2Br202 . The  silver 
salt  falls,  on  the  addition  of  argentic  nitrate  to  an  aqueous  solution  of 
the  acid,  in  flattened  jagged  needles  which  are  readily  decomposed  by 
heat.  They  could,  however,  be  dried  over  sulphuric  acid  without  any 
essential  decomposition,  as  is  shown  by  the  following  analysis  : — 

0.4885  grm.  of  substance  gave  by  precipitation  with  HBr  0.2231 


grm.  AgBr. 

Calculated  for  AgC3HCl2Br202 . 
26.46 


Found. 

26.23 


Ag 


Baric  a Dichlordibrompropionate , Ba(C3HCl2Br202)2 . The  barium 
salt  we  made  by  neutralizing  a cold  aqueous  solution  of  the  acid  with 
baric  carbonate.  On  evaporation  at  ordinary  temperatures  it  crys- 
tallized in  long  branching  needles,  which  when  dried  by  exposure  to 
the  air  did  not  lose  materially  in  weight  over  sulphuric  acid,  and  con- 
tained a percentage  of  barium  corresponding  to  the  anhydrous  salt. 

I.  0.5069  grm.  of  the  air-dried  salt  gave  0.1606  grm.  BaS04 . 

II.  0.5239  grm.  of  the  air-dried  salt  gave  0.1676  grm.  BaS04 . 


Calculated  for  Ba(C3HCl2Br202)2 . 


Found. 

I.  II. 

18.58  18.81 


Ba 


18.59 


OF  ARTS  AND  SCIENCES. 


147 


The  barium  salt  is  decomposed  by  warming,  its  solution  giving 
products  similar  to  those  obtained  in  the  same  way  from  tetrabrom- 
propionic  acid.  This  decomposition,  however,  we  have  not  as  yet 
studied  further. 


Dichlordibrompropionic  Acid, 

Although  dibromacrylic  acid  assumes  a molecule  of  bromine  so 
readily,  we  found  at  first  great  difficulty  in  preparing  the  corresponding 
addition  product  with  chlorine.  If  chlorine  gas  is  passed  into  melted 
dibromacrylic  acid  it  is  gradually  taken  up  and  the  melting-point  of 
the  acid  is  slowly  changed.  After  long-continued  action  a considerable 
quantity  of  the  dichlordibrompropionic  acid  is  formed,  but  so  contam- 
inated with  oily  by-products  that  its  purification  is  a matter  of  some 
difficulty.  This  addition  of  chlorine  is,  however,  rapidly  and  neatly 
accomplished  if  the  reaction  is  allowed  to  proceed  in  direct  sunlight 
at  100°.  When  at  this  temperature  the  melted  acid  becomes  nearly 
solid  with  separating  crystals  of  the  addition  product,  the  chlorination 
is  interrupted.  The  product  which  we  obtained  in  this  way  from 
pure  dibromacrylic  acid  melting  at  85-86°  was  purified  by  crystalliza- 
tion first  from  carbonic  disulphide  and  finally  from  chloroform.  On 
analysis  it  gave  the  following  results  : — 

I.  0.5183  grm.  substance  gave  0.2335  grm.  C02  and  0.0431  grm. 
H20. 

II.  0.1547  grm.  substance  gave  0.3400  grm.  AgCl  -f-  AgBr.  From 
this  by  reduction  was  obtained  0.2214  grm.  A g. 

Calculated  for  (C3H2Cl2Br202).  Found. 


I.  II. 


c 

11.96 

12.13 

H 

0.66 

0.92 

Cl 

23.59 

23.37 

Br 

53.15 

53.21 

This  ft  dichlordibrompropionic  acid  crystallizes  in  oblique  prisms 
which  melt  at  118-120°,  and  in  its  behavior  with  solvents  closely 
resembles  the  a acid.  In  water,  alcohol,  or  ether  it  dissolves  very 
easily,  but  with  somewhat  more  difficulty  in  carbonic  disulphide,  chlo- 
roform, or  benzol.  The  solution  in  carbonic  disulphide  gave  by  slow 
evaporation  well-developed  crystals  whose  elements  .Dr.  W.  H.  Mel- 
ville kindly  determined. 


148 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Crystalline  Form  of  p Dichlordibrompropionic  Acid. 


Monoclinic  System . 
Forms,  {100}  {110}  Jill}  {102} 

Elements  : Clinodiagonal  a = 2.393 

Orthodiagonal  b = 1 

Vertical  axis  c = 1.731 

Angle  of  axes  XZ  = 46°  9 


Angles  between  Normals. 


Observed. 

Calculated. 

110 

and  110  = 

60°  IF  \ 

111 

u 

110  = 

42°  24J'  [ 

■ Fundamental  Angles. 

111 

u 

110  = 

40°  33  J' ) 

TOO 

a 

T10  = 

59°  53' 

59°  54J' 

111 

a 

111  ~ 

120°  V 

119°  56' 

100 

u 

111  = 

00 

00 

o 

Or 

88°  47' 

102 

u 

T10  = 

102°  21' 

102°  23; 

102 

u 

110  = 

78°  5' 

77°  37' 

102 

a 

111  = 

63°  44' 

63°  42J' 

The  difference  between  the  a and  ft  acids  was  further  confirmed  by 
a study  of  the  silver  and  barium  salts. 

Argentic  ft  Dichlordibrompropionate , AgC3HCl2Br202 . The  silver 
salt  is  precipitated  in  the  form  of  short,  thick,  pointed  prisms  when 
argentic  nitrate  is  added  to  an  aqueous  solution  of  the  acid.  It  is 


OF  ARTS  AND  SCIENCES. 


149 


readily  decomposed  by  heat,  but  may  be  dried  for  analysis  over  sul- 
phuric acid. 

0.4950  grm.  of  the  salt  gave  on  precipitation  with  HC1  0.1731  grm. 

AgCl. 

Calculated  for  AgC3HCl2Br202 . Found. 

Ag  26.46  26.31 

Baric  ft  Dichlordibrompropionate , Ba(C3HCl2Br202)2 . 2H20.  The 
barium  salt  which  we  made  by  neutralizing  an  aqueous  solution  of  the 
acid  with  baric  hydrate  crystallized  on  spontaneous  evaporation  of  its 
solution  in  long  radiating  needles  which  were  very  soluble  in  cold 
water.  When  dried  by  exposure  to  the  air  the  salt  proved  to  contain 
two  molecules  of  water  which  it  lost  over  sulphuric  acid. 

I.  1.6201  grm.  of  the  air-dried  salt  lost  over  H2S04  0.0705  grm. 

H20. 

II.  1.5443  grm.  of  the  air-dried  salt  lost  over  H2S04  0.0731  grm. 

H20. 

Calculated  for  Ba(C3HCl2Br202)2 . 2 H20.  Found.^ 

H20  4.66  4.35  4.74 

0.8236  grm.  of  the  salt  dried  over  H2S04  gave  0.2619  grm.  BaS04. 

Calculated  for  Ba(C3HCl2Br202)2 . Found. 

Ba  18.59  18.69 


These  results  prove  that  the  a and  § dichlordibrompropionic  acids 
described  are  essentially  different. 


Dichlordibrompropionic  Acid. 

a 

P 

System  of  Crystallization 

Melting-point  

Barium  salt 

Triclinic. 

94-95° 

Ba(C3HBr2Cl202) 

Monoclinic. 

118-120° 

Ba(C3HBr2Cl202)2 . 2 H20. 

The  barium  salt  was  readily  decomposed  by  warming  its  aqueous 
solution.  Baric  chloride  and  carbonic  dioxide  were  formed  together 
with  a colorless  oil  which  undoubtedly  was  a dibromchlorethylen. 
With  bromine  this  oil  gave  a solid  addition  product,  which,  however, 
we  have  not  as  yet  prepared  in  quantity  sufficient  for  complete  purifi- 
cation and  identification. 


150 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


V.  On  the  Constitution  of  the  Substituted  Acrylic  and 

Propionic  Acids. 

By  Henky  B.  Hill. 

Within  a few  years  the  number  of  substituted  acrylic  and  pro- 
pionic acids  known  has  been  largely  increased,  and  yet  the  constitution 
of  but  few  of  these  can  be  said  to  be  satisfactorily  established.  In  a 
previous  communication  I was  led  to  adopt  provisionally  for  muco- 
bromic  acid  the  formula,  — 

CBr2  — CHO 

i 

— C — COOH 

which  explained  its  connection  with  maleic  acid,  in  whose  molecule  the 
researches  of  Fittig  had  shown  the  provable  existence  of  a dyad 
carbon  atom.  The  structure  of  the  related  dibromacrylic  acid  was 
then  naturally  expressed  by  the  formula, — 

CBr2H 

I 

C = 

i 

COOH 

against  which  at  the  time  nothing  more  convincing  than  a belief  in  its 
improbability  could  be  urged.  The  relations  which  Andrews  and  I 
have  shown  to  exist  between  this  same  acid  and  two  different  tribrom- 
propionic  acids  prove,  however,  that  this  formula  is  incorrect.  An  acid 
with  this  structure  could  be  formed  from  but  a single  tribrompropionic 
acid,  and  must  of  necessity  give  this  same  tribrompropionic  acid  by  the 
addition  of  hydrobromic  acid.  The  same  objection  also  applies  with 
equal  force  to  the  other  two  conceivable  formulas  for  dibromacrylic 


acid  which  contain  dyad  carbon,  — 

= CH 

= CBr 

i 

CBr2  and 

CHBr 

COOH 

COOH 

OF  ARTS  AND  SCIENCES.  151 

and  these  must  consequently  be  rejected.  There  remain  therefore  for 
the  acid  in  question  but  two  possible  formulae,  — 

CBr2  CHBr 

II  II 

CH  and  CBr 

l i 

COOH  COOH 


The  formation  of  two  isomeric  dichlordibrompropionic  acids  by  the 
addition  of  chlorine  to  the  dibromacrylic  acid  and  of  bromine  to  the 
analogous  dichloracrylic  acid,  as  Mabery  and  I have  shown,  would 
seem  again  to  be  decisive  in  favor  of  the  first  of  these  formulae,  since 
its  adoption  would  give,  — 


CBr2Cl 

CCl2Br 

CHC1 

and 

CHBr 

COOH 

COOH 

as  the  structure  of  the  two  isomeric  dichlordibrompropionic  acids, 
while  the  second  formula  would  give  in  either  case  the  same  com- 
pound, — 

CHBrCl 

I 

CBrCl 

i 

COOH 

Although  it  was  by  no  means  impossible  that  a molecular  rearrange- 
ment had  taken  place  in  one  of  these  two  reactions,  still  it  seemed 
improbable,  since  the  reactions  were  apparently  neat,  and  in  the  treat- 
ment with  chlorine,  where  such  a change  would  be  more  naturally 
expected,  no  bromine  could  be  detected  in  the  escaping  chlorine. 

On  the  other  hand  the  adoption  of  the  formulae,  — 


CBr2 

CC12 

II 

II 

CIi 

•and 

CH 

COOH 

COOH 

for  the  derivatives  of  mucobromic  and  mucochloric  acids  presented 
difficulties  quite  as  serious.  In  the  first  place  the  dichloracrylic  acid 


152  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

of  Wallach  had  been  proved  beyond  all  doubt  to  be  different  from 
that  which  Bennett  and  I had  described  by  a comparison  of  the  crys- 
talline form  of  the  two  acids,  and  it  would  follow  then  that  Wallach’s 
acid  could  not  have  the  formula  he  assigned  to  it.  The  formation  of 
an  acid  with  different  structure  from  chloralid  could,  however,  be 
explained  upon  the  assumption  that  the  chlorpropiolic  acid  was  the 
first  product  of  the  reduction,  and  that  this  passed,  on  the  one  hand 
by  the  addition  of  hydrogen,  into  the  0 chloracrylic  acid,  and  on  the 
other  hand  formed  dichloracrylic  acid  by  addition  in  the  subsequent 
treatment  with  strong  hydrochloric  acid  which  Wallach  prescribes.* 
Although  this  hypothesis  was  far  from  satisfactory,  it  seemed  to  me 
hardly  more  improbable  than  that  a similar  molecular  rearrangement 
had  taken  place  in  the  reaction  which  had  come  under  my  own  obser- 
vation. 

Still  another  difficulty  was  to  be  found  in  the  formation  of  the 
dibromacrylic  acid  in  question  from  the  tribrompropionic  acid  melting 
at  92°,  which,  if  the  ordinarily  accepted  formula  for  the  latter,  — 

CH2Br 

CBr2 

i 

COOH 

were  correct,  would  prove  the  incorrectness  of  the  formula  assumed. 
I was  at  first  unable  to  attach  any  great  importance  to  this  argument, 
inasmuch  as  the  constitution  of  the  monobromacrylic  acids  was  ex- 
tremely uncertain.  For  although  the  discovery  by  Wallach  of  the 
ft  monobromacrylic  acid  melting  at  115°  had  rendered  the  constitution 
of  the  a and  monobromacrylic  acids  of  Tollens  extremely  doubtful, 
it  by  no  means  proved  their  identity. 

Erlenmeyer  has,  however,  recently  shownf  that  the  a and  ft  acids  of 
Tollens,  as  well  as  their  potassium  salts,  crystallize  in  identical  forms, 
and  the  structure  of  the  tribrompropionic  acid  melting  at  92°  is  there- 
fore put  upon  quite  another  footing.  Since  the  same  (a)  monobrom- 
acrylic acids  can  be  made  from  a dibrompropionic  and  also  from  its 
isomer,  the  a ft  dibrompropionic,  it  follows  that  this  acid  must  have  the 
structure,  — 


* Ann.  Chem.  u.  Pharm.,  xcxiii.  7. 
t Berichte  der  deutsch.  chem.  Gesellsch.,  xiv.  1867. 


OF  ARTS  AND  SCIENCES. 


153 


CH 

ii 

CBr 

i 

COOH 

and  the  tribrompropionic  acid  made  from  it  by  the  addition  of  bromine 
must  of  course  have  the  corresponding  form,  — 

CH2Br 

CBr2 

i 

COOH 


Since  the  formulae  with  dyad  carbon  are  in  this  case  excluded,  there 
remains  for  the  dibromacrylic  acid  in  question  onlv  the  structure,  — 

CHBr 

II 

CBr 

l 

COOH 

Although  this  conclusion  is  directly  at  variance  with  the  results 
which  Mabery  and  I obtained  in  the  study  of  the  dichlordibrompro- 
pionic  acids,  it  must  be  confessed,  I think,  that  it  is  probably  correct. 
Still,  since  its  adoption  presents  undoubted  difficulties,  I shall  endeavor 
to  bring  more  direct  experimental  evidence  as  to  its  correctness. 

The  dibromacrylic  acid  of  Fittig  and  Petri,  which,  as  Mabery  and  I 
have  shown,  can  be  made  from  brompropiolic  acid,  would  naturally 
have  the  form,  — 

CBr2 

M 

CH 

i 

COOH 

and  the  acids  made  in  the  same  way  containing  two  halogens  the 
corresponding,  — 


CBrI 

CBr  Cl 

II 

II 

CH 

CH 

COOH 

COOH 

154 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


The  tribrompropionic  acid  melting  at  118°  would  be  written,  — 

CHBr2 

I 

CHBr 

COOH 

and  the  tetrabrompropionic  acid  would  have  the  form,  — 

CHBr2 

CBr2 

i 

COOH 


VI.  Crystalline  Form  of  Tribromacrylic  Acid. 
By  W.  H.  Melville. 


Monoclinic  System . 

Forms,  {010}  {110}  {011}  {101}  fTOl}  {021}  ; the  last  three 
forms  being  rarely  observed. 

Elements  : Clinodiagonal  a = 0.502 

Orthodiagonal  b = 1. 

Vertical  axis  c = 0.559 

Angle  of  axes  XZ  = 64°  29  J7 


\ 


OF  ARTS  AND  SCIENCES. 


155 


Angles  between  Normals, 


Observed.  Calculated. 


010  and  110  = 65°  38/) 

010  “ Oil  = 63°  14'  > Fundamental  angles, 

011  “ 110  = 57°  35') 


T10  “ TIO  = 48°  42'  48°  44' 

010  “ 021  = 44°  41'  44°  45' 

021  “ Oil  = 18°  33'  18°  29' 

011  “ 011  =53°  33'  53°  32' 

Oil  “ T01  = 42°  25'  42°  23 


Since*  Dr.  F.  Becke’s  results  of  the  determination  of  the  same 
crystals  do  not  appear  to  be  reconcilable  with  the  above,  a comparison 
is  important.  The  forms  r (110)  l (1T0)  when  referred  to  the  crys- 
tals which  I have  examined,  correspond  to  {021},  and  o (111),  u 
(III)  would,  if  present,  occur  as  the  prism  {120}.  Among  the  many 
sets  of  crystals  submitted  to  me  I have  never  observed  the  prism 
{120}.  The  following  table  shows  a few  of  the  angles  both  actual 
and  hypothetical,  assuming  that  the  crystals  are,  monoclinic  in  form, 
when  compared  with  Becke’s  corresponding  measurements. 


Monoclinic. 

(010)  A (021)  = 44°  41' 
(021)  A (021)  = 90°  38' 
(021)  A (010)  = 44°  41' 
(010)  A (120)  = 47°  45 1' 
(120)  A (120)  ==  84°  28 1' 
(IE0)a(0T0)  = 47°  45 1' 
(010)  A (021)  ==  44°  41' 
(010)  A (120)  = 47°  45|' 


Becke. 

44°  42'  = hr 
91°  11'  = rl 
44°  13'  = bl 
47°  19'  = bu 
84°  55'  = ou 
48°  10'  = bo 

44°  27  J'  = mean  of  br  and  bl 
47°  441'  „ „ bu  „ bo 


The  following  measurements,  which  were  obtained  from  a single 
crystal,  appear  to  establish  conclusively  the  system  of  crystallization  as 
monoclinic. 


* Sitzungsberichte  der  kaiser.  Akad.  der  Wissensch.,  Band  lxxxiii.  286-287, 
Wien,  1881. 


156 


PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Zone  [010,  110] 


Zone  [010,  Oil] 


(110)  A (010)  = 65°  33' 
(OIO)A(HO)  = 65°  44' 

(110)  A (TO)  = 48°  28' 
(TTO)a(OTO)  = 65°  52J' 

(010)  A (HO)  = 65°  35' 

(110)  A (HO)  — 48°  44' 

359°  561' 

(010)  A (021)  ==  44°  41'  ) 

(021)  A (Oil)  = 18°  30'  J 11 

(011)  a (Oil)  = 54°  5' 
(OII)a(OTO)  — 62°  56' 

180°  12' 

(110)  A (Oil)  = 122°  32 J' 
(Oll)A(TlO)  = 57°  18|' 

179°  51' 

(OTl)  A (HO)  = 57°  21' 


The  crystal  face  (OTl)  was  somewhat  imperfect,  so  that  the  reflected 
image  was  extended  in  width.  Hence,  the  angles  between  (OTl)  and 
adjacent  planes  are  rendered  uncertain,  but  only  by  the  small  va’ae 
of  7'  or  8'.  All  the  other  faces  gave  exceedingly  sharp  reflections. 

From  these  considerations  upon  the  system  in  which  tribromacrylic 
acid  crystallizes,  it  will  appear  that  we  have  to  deal  with  a question 
of  small  differences,  and  that  in  consequence  of  the  very  prominent 
monoclinic  habit,  we  are  justified  in  making  these  crystals  monoclinic, 
and  not  triclinic,  as  Becke  has  determined  them. 


